US4823131A - Radar reflector - Google Patents

Radar reflector Download PDF

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Publication number
US4823131A
US4823131A US07/075,998 US7599887A US4823131A US 4823131 A US4823131 A US 4823131A US 7599887 A US7599887 A US 7599887A US 4823131 A US4823131 A US 4823131A
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United States
Prior art keywords
radar
reflecting
housing
reflecting elements
strings
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
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US07/075,998
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English (en)
Inventor
Stephen W. Bell
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Individual
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Individual
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Priority claimed from GB868617912A external-priority patent/GB8617912D0/en
Priority claimed from GB868617916A external-priority patent/GB8617916D0/en
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Publication of US4823131A publication Critical patent/US4823131A/en
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Expired - Fee Related legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
    • H01Q15/14—Reflecting surfaces; Equivalent structures
    • H01Q15/18—Reflecting surfaces; Equivalent structures comprising plurality of mutually inclined plane surfaces, e.g. corner reflector

Definitions

  • This invention relates to reflectors for reflecting radar signals so that they return substantially parallel to their angle of incidence.
  • the simplest of these is the well known octahedral reflector which comprises three sheets of electrically conducting material arranged mutually orthogonally to one another and intersecting one another to provide eight trihedral re-entrant corners having a common geometric origin.
  • Each trihedral re-entrant corner reflects a radar beam which enters that corner reasonably close to its axis at substantially its incident angle.
  • the incident radar signal arrives at an angle with respect to the axis of the trihedral re-entrant corner reflector the magnitude of the signal reflected back along the path of the incident signal falls off rapidly and falls off even more rapidly at incident angles greater than 20°.
  • radar reflectors consisting of a single hand or double handed helical array of trihedral re-entrant corner reflecting elements have been produced.
  • Such radar reflectors are illustrated in, for example, GB-A No. 681666 and EP-A No. 0000447, respectively.
  • the origins of the trihedral reflecting elements are located around a cylinder.
  • Such reflectors are generally successful particularly for use on sailing boats in which they can be hoisted high into the rigging and so hoisted to a considerable height above the surface of the sea. They have also been used for other marine purposes such as navigational buoys.
  • a radar reflector comprises a hollow, generally spherical or conical radar transmitting housing containing a radar reflecting assembly having a number of trihedral cube corner reflecting elements arranged in strings one above the other and with a number of the strings arranged side-by-side around the inside of the housing.
  • the radar reflector in accordance with this invention is particularly useful with navigational buoys.
  • the radar reflector may form at least part of the buoy and, in this case the hollow housing may be formed by at least the upper part of a conventional can or ogive-shaped buoy which projects above the surface of the water.
  • the radar reflector is provided as a top mark for a navigational buoy.
  • Navigational buoys particularly those used in the Cardinal system of buoyage have top marks formed by combinations of spheres and cones which serve to identify the nature of the hazzard and its relative direction from the position of the buoy. Such top marks are mounted on posts projecting upwards from a main body of the buoy.
  • the housing of the radar reflector is preferably made from plastics material such as polyethylene and is typically made by a rotational moulding process in which, the radar reflecting assembly is mounted inside a hollow two-part mould which is then heated and into which is placed a shot of powdered plastics material. The mould is then rotated in all directions so forming a continuous plastics lining covering over the entire inner surface of the mould. After subsequent cooling and demoulding a join free continuous housing is obtained.
  • the size of the radar reflecting elements in each string may vary.
  • the element at one end of each string may be the smallest and that at the other end the largest; and, when the housing is generally spherical the largest element may be in the middle of each string and smaller elements located at both ends.
  • a generally spherical reflector may also be filled by two generally conical radar reflecting assemblies arranged base to base.
  • a radar reflector in accordance with this invention has a sufficiently fine structure of its 4 ⁇ polar diagram to be capable of resolving a narrow angle between incident beams and consequently enables a detectable return to be generated even when the reflector is mounted close to the surface of the sea under conditions of high sea surface specular reflection caused by a calm sea or ice.
  • This effect is further enhanced by typically using two top marks on each buoy and having both formed as radar reflectors in accordance with this invention.
  • the provision of the two radar reflectors one above the other increases the lateral separation between reflecting elements and provides phase distinct paths from which a detectable return is more certain.
  • the radar reflecting assembly comprises strings of reflecting elements with the origins of all of the reflecting elements lying on and being arranged around a frusto-conical surface and with all of the reflecting elements facing outwards.
  • the reflecting assembly is preferably formed from electrically conducting sheet material folded into a pleated frusto-conical body, adjacent outwardly facing folds including a right angle, and two or more separator plates located between the adjacent outwardly facing folds and normal to the fold line between them to form the cube-corner reflecting elements.
  • this reflecting assembly it is the cone angle of the cone containing the fold lines including a right angle, the inner fold lines, which, together with the spacing of the separator plates, determines its performance.
  • this cone angle is within a range of 45° to 55° and it is further preferred that it is between 50° and 62°.
  • a cone angle of exactly 54.7° ensures that when the radar reflecting array is strictly vertical the centre of the reflection lobe from each reflecting element is horizontal.
  • the angle of the cone containing the other fold lines of the pleated array, the outer fold lines is preferably matched to that of the inside of the housing.
  • this type of reflector is preferred where it can be mounted so as to be substantially vertical in use.
  • the phase difference between the radar signals reflected from adjacent reflecting elements does not differ by a whole number of wavelengths.
  • a point can be reached where there is an odd number of half wavelength's difference between the radar signals reflected from adjacent elements and then they destructively interfere to cancel the return echo.
  • a second example of reflecting assembly is used when it heels from the vertical in use.
  • the radar reflecting assembly comprises at least three strings of single or double handed helical reflecting element arrays arranged side-by-side.
  • the axes of the strings of reflecting element arrays may each be generally straight and in this case the axes may be arranged substantially parallel to one another or they may be arranged at an angle to one another, so that their axes lie on a frusto-conical surface.
  • each string is formed by folding a strip of electrically conducting material into a number of trapezium-shaped plates each of which is folded at right angles to its neighbours and then fixing separator plates normally to the fold lines in between each adjacent pair of trapezium-shaped plates to form cube-corner reflecting elements.
  • each of the arrays receive incident radar radiation at any instant irrespective of its incident angle and ensures that a larger radar return or echo is generated simply as a result of reflections from the at least two reflectors.
  • each of the arrays with the axes of their cube corner reflectors oriented in different directions this increases the likelihood of the incident radiation approaching at least one reflecting element axially.
  • each string may be made by folding a tapering strip of sheet material.
  • the strip may taper from one end to the other so that, after folding the elements at one end of the string are smaller than the elements at the other end of the string.
  • the strip may be widest at its centre and taper to both ends to provide a string with the largest reflecting element in the middle and the smallest at both ends.
  • the former of these is more suited to construction of a generally frusto-conical form of the radar reflecting assembly and the latter to a generally spherical form of radar reflecting assembly. Consequently it is preferred that the former is used with a generally conical housing and the latter used with a spherical housing.
  • each helical string includes only five folds with a projected half twist angle of substantially 11°. This provides each string with a non-uniform reflection characteristic around its azimuth. With this arrangement the strings are arranged with their parts providing the greatest reflection pointing outwards.
  • FIG. 1 is a side elevation of a navigational buoy with top marks including radar reflectors
  • FIG. 2 is a side elevation of alternative top marks
  • FIG. 3 is a partly sectioned side elevation of a conical top mark including a first example of radar reflecting assembly
  • FIG. 4 is a perspective view of the first example of radar reflecting assembly
  • FIG. 5 is a side elevation of a second example of radar reflecting assembly
  • FIG. 6 is a perspective view of the second example of radar reflecting assembly
  • FIG. 7 is a plan of a blank for forming one string of the second example of radar reflecting assembly.
  • FIG. 8 is a plan of a blank for forming a third example of radar reflecting assembly.
  • a navigational buoy for use in the Cardinal system comprises an ogive-shaped body 1 moored to the sea bed by mooring chains 2.
  • a mounting post 3 projects vertically from the body 1 and carries spherical top marks 4.
  • Conical top marks 5, shown in FIG. 2 may be mounted on the post 3.
  • the cones 5 are mounted as shown in FIG. 2 with their points together, mounted with both of their points pointing upwards or downwards or mounted with their bases together to indicate that the buoy is to the west, the north, the south or the east, respectively, of the navigational hazard.
  • the top marks 4 and 5 each comprise a hollow, radar transparent housing 6 formed around a tube 7 with a radar reflecting assembly 10 mounted on the tube 7 and located inside the housing 6.
  • the radar reflecting assembly 10 is formed from sheet metal such as sheet aluminium and the tube 7 is also formed from aluminium.
  • the tube 7 is fitted over the mounting post 3.
  • the housing 6 is formed by rotational moulding with the reflecting assembly 10 and tube 7 fixed inside a rotational mould into which a charge of moulding powder, such as polyethylene, is inserted and the mould heated and rotated in all directions to coat the inner surface of the mould with polyethylene to form a continuous join-free housing 6.
  • the radar reflecting assembly 10 may buttress the side wall of the housing 6.
  • the radar reflecting assembly 10 can also be located inside the part of the body 1 of the buoy which projects above the surface of the sea as indicated in FIG. 1.
  • the ogive-shaped top portion of the body of the buoy at least, is formed from radar transparent material.
  • the first example of radar reflecting assembly 10 is shown more clearly in FIG. 4 and comprises a sheet of material folded into a number of similar but laterally reversed trapezium-shaped panels 11 and 12 with the complete assembly having a generally frusto-conical form. A right angle is included between each of the panels 11 and 12 and three separator plates 13, 14 and 15 are fixed between each adjacent pair of panels 11 and 12 to form upright strings 16 of three cube-corner reflecting elements 17.
  • a trihedral cube-corner reflecting element is thus formed by each separator plate 13, 14, and 15 and the portions of the panels 11 and 12 adjacent it.
  • Each of these trihedral cube-corner reflecting elements 17 acts as a retroreflector to return incident radar signal.
  • Inner folds 18 formed between adjacent plates 11 and 12 lie on a cone having an angle of 54.7 degrees to ensure that when the axis of the cone is vertical the centre of the reflection lobe from each reflecting element 17 lies in a horizontal plane so that the maximum return is provided by the radar reflecting assembly 10 with a generally horizontal incident beam.
  • Outer folds 19 forming the external join between the plates 11 and 12 all lie substantially on the surface of a cone having the same core angle as the housing 6 and the outermost edges of the separator plates 13, 14 and 15 may engage the inner surface of the housing 6.
  • the second example of radar reflecting assembly shown in FIGS. 5 and 6 comprises three similar, equiangularly spaced helical cube corner reflecting arrays or strings 20.
  • Each array 20 is formed by folding a generally tapering strip of material, as shown in FIG. 7 into six trapezium-shaped plates 21, 22, 23, 24, 25 and 26 with right angled corners being formed between each adjacent pair of plates.
  • the dotted lines indicate a fold in one direction and the chain-dotted lines indicate a fold in the opposite direction.
  • Separator plates 27 are located midway along each fold and lie in a plan normal to the fold line.
  • each of the separator plates 27 is shaped so as to enable the entire reflecting assembly to be fitted inside a conical envelope formed by the housing 6.
  • the half-twist angle of the helical array that is half of the angle between the projections of two adjacent fold lines onto a horizontal plane, is equal to 11 degrees. This provides each helical cube corner reflecting array 20 with more cube corner reflecting elements 17 pointing generally outwards away from the other reflectors than pointing inwards.
  • the reflecting arrays 20 are equiangularly spaced around the azimuth.
  • blanks 28 such as shown in FIG. 8 are formed into helical cube corner reflecting arrays.
  • the helical cube corner reflecting arrays have a greater width in the middle length and so are more suited to being located inside a spherical housing 6 to form a spherical top mark 4.
  • one generally conical reflecting array can be fitted inside each spherical top mark 4 or, preferably, two generally conical arrays arranged base to base are located inside each spherical top mark 4.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Aerials With Secondary Devices (AREA)
US07/075,998 1986-07-22 1987-07-21 Radar reflector Expired - Fee Related US4823131A (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB8617912 1986-07-22
GB868617912A GB8617912D0 (en) 1986-07-22 1986-07-22 Radar reflector
GB868617916A GB8617916D0 (en) 1986-07-22 1986-07-22 Radar reflector
GB8617916 1986-07-22

Publications (1)

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US4823131A true US4823131A (en) 1989-04-18

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US07/075,998 Expired - Fee Related US4823131A (en) 1986-07-22 1987-07-21 Radar reflector

Country Status (5)

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US (1) US4823131A (de)
EP (1) EP0255284B1 (de)
DE (1) DE3784579T2 (de)
ES (1) ES2040254T3 (de)
FI (1) FI86342C (de)

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5784196A (en) * 1996-10-28 1998-07-21 The United States Of America As Represented By The Secretary Of The Army Active/passive signature enhancer (APSE)
US5812331A (en) * 1992-12-08 1998-09-22 Centre National D'etudes Spatiales Reflector for a polarimetric radar in particular for use as a calibrator or as a beacon
US20140368373A1 (en) * 2011-12-20 2014-12-18 Sadar 3D, Inc. Scanners, targets, and methods for surveying
US20150130651A1 (en) * 2013-11-10 2015-05-14 Chris Mogridge Passive Radar Activated Anti-Collision Apparatus
US10014587B1 (en) * 2011-12-08 2018-07-03 The United States Of America As Represented By The Secretary Of The Navy Retroreflecting chaff for laser defense
US20190252791A1 (en) * 2018-02-09 2019-08-15 The Boeing Company Inflatable Radar Decoy System and Method
US11249178B2 (en) 2019-01-02 2022-02-15 Fractal Antenna Systems, Inc. Satellite orbital monitoring and detection system using fractal superscatterer satellite reflectors (FSR)
US11280659B2 (en) * 2019-08-23 2022-03-22 Endress+Hauser SE+Co. KG Reflector for radar-based fill level detection
US12077179B2 (en) 2017-02-23 2024-09-03 Vehicle Radar Guidance, Llc Vehicle guidance system

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE9402047L (sv) * 1994-06-13 1995-12-14 Contractor Tools Ab Förfarande och anordning för fjärrstyrning av en eller flera arbetsmaskiner
DE102007043460B4 (de) * 2007-09-12 2012-08-30 Hans-Heinrich Götting jun. Verfahren zur Navigation eines Fahrzeuges
DE102018211363A1 (de) * 2018-07-10 2020-01-16 Bayerische Motoren Werke Aktiengesellschaft Spurführung eines Kraftfahrzeugs auf einer Fahrspur

Citations (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2721998A (en) * 1950-05-13 1955-10-25 Gasaccumulator Svenska Ab Radar reflector
DE1014610B (de) * 1955-03-29 1957-08-29 Julius & August Erbsloeh Komma Radar-Reflektor
GB812376A (en) * 1956-01-03 1959-04-22 Anthony Edgar Porter Improvements in radar reflectors
US3103662A (en) * 1958-06-03 1963-09-10 Dunlop Rubber Co Inflatable eight-corner reflector
US3310804A (en) * 1963-06-18 1967-03-21 Joseph B Brauer Isotropic microwave reflector
GB1468516A (en) * 1974-09-05 1977-03-30 Secr Defence Reflecters for electromagnetic radiation
US4073568A (en) * 1975-11-26 1978-02-14 Ferro Corporation Retroreflector units with three mutually perpendicular surfaces defining a trihedral angle of a rectangular parallelepiped
US4096479A (en) * 1977-04-14 1978-06-20 The United States Of America As Represented By The Secretary Of The Navy Radar significant target
US4104634A (en) * 1974-01-03 1978-08-01 The Commonwealth Of Australia Ground plane corner reflectors for navigation and remote indication
EP0000447A1 (de) * 1977-07-15 1979-01-24 John Hewitt Firth Radarreflektor
US4352106A (en) * 1979-09-17 1982-09-28 Firth John H Radar reflectors
GB2145656A (en) * 1983-09-02 1985-04-03 Univ London Method of rotational casting
DE8430647U1 (de) * 1984-10-18 1985-04-04 Wittig, Karl-Ernst, 4100 Duisburg Radarreflektor
US4551726A (en) * 1982-07-30 1985-11-05 Berg Richard M Omni-directional radar and electro-optical multiple corner retro reflectors

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL77990C (de) * 1950-05-13

Patent Citations (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2721998A (en) * 1950-05-13 1955-10-25 Gasaccumulator Svenska Ab Radar reflector
DE1014610B (de) * 1955-03-29 1957-08-29 Julius & August Erbsloeh Komma Radar-Reflektor
GB812376A (en) * 1956-01-03 1959-04-22 Anthony Edgar Porter Improvements in radar reflectors
US3103662A (en) * 1958-06-03 1963-09-10 Dunlop Rubber Co Inflatable eight-corner reflector
US3310804A (en) * 1963-06-18 1967-03-21 Joseph B Brauer Isotropic microwave reflector
US4104634A (en) * 1974-01-03 1978-08-01 The Commonwealth Of Australia Ground plane corner reflectors for navigation and remote indication
GB1468516A (en) * 1974-09-05 1977-03-30 Secr Defence Reflecters for electromagnetic radiation
US4073568A (en) * 1975-11-26 1978-02-14 Ferro Corporation Retroreflector units with three mutually perpendicular surfaces defining a trihedral angle of a rectangular parallelepiped
US4096479A (en) * 1977-04-14 1978-06-20 The United States Of America As Represented By The Secretary Of The Navy Radar significant target
EP0000447A1 (de) * 1977-07-15 1979-01-24 John Hewitt Firth Radarreflektor
US4352106A (en) * 1979-09-17 1982-09-28 Firth John H Radar reflectors
US4551726A (en) * 1982-07-30 1985-11-05 Berg Richard M Omni-directional radar and electro-optical multiple corner retro reflectors
GB2145656A (en) * 1983-09-02 1985-04-03 Univ London Method of rotational casting
DE8430647U1 (de) * 1984-10-18 1985-04-04 Wittig, Karl-Ernst, 4100 Duisburg Radarreflektor

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5812331A (en) * 1992-12-08 1998-09-22 Centre National D'etudes Spatiales Reflector for a polarimetric radar in particular for use as a calibrator or as a beacon
US5784196A (en) * 1996-10-28 1998-07-21 The United States Of America As Represented By The Secretary Of The Army Active/passive signature enhancer (APSE)
US10014587B1 (en) * 2011-12-08 2018-07-03 The United States Of America As Represented By The Secretary Of The Navy Retroreflecting chaff for laser defense
US20140368373A1 (en) * 2011-12-20 2014-12-18 Sadar 3D, Inc. Scanners, targets, and methods for surveying
US20150130651A1 (en) * 2013-11-10 2015-05-14 Chris Mogridge Passive Radar Activated Anti-Collision Apparatus
US12077179B2 (en) 2017-02-23 2024-09-03 Vehicle Radar Guidance, Llc Vehicle guidance system
US20190252791A1 (en) * 2018-02-09 2019-08-15 The Boeing Company Inflatable Radar Decoy System and Method
US11249178B2 (en) 2019-01-02 2022-02-15 Fractal Antenna Systems, Inc. Satellite orbital monitoring and detection system using fractal superscatterer satellite reflectors (FSR)
US11555907B2 (en) 2019-01-02 2023-01-17 Fractal Antenna Systems, Inc. Satellite orbital monitoring and detection system using fractal superscatterer satellite reflectors (FSR)
US11280659B2 (en) * 2019-08-23 2022-03-22 Endress+Hauser SE+Co. KG Reflector for radar-based fill level detection

Also Published As

Publication number Publication date
FI86342B (fi) 1992-04-30
DE3784579D1 (de) 1993-04-15
FI86342C (fi) 1992-08-10
FI873171A0 (fi) 1987-07-17
EP0255284A1 (de) 1988-02-03
FI873171A (fi) 1988-01-23
DE3784579T2 (de) 1993-10-07
ES2040254T3 (es) 1993-10-16
EP0255284B1 (de) 1993-03-10

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